1. Field of the Invention
This invention relates to a radio module connected to an antenna device, and a radio communication apparatus equipped with the radio module, and more particularly to a radio communication apparatus used close to or in contact with a human body, such as a portable telephone, PDA (Personal Digital Assistant), cordless telephone, transceiver, etc.
2. Description of the Related Art
In general, mobile communication apparatuses, represented by portable telephones, use an antenna device including a whip antenna and a helical antenna. The antenna device is formed by attaching an element of the helical antenna to the tip of the element of the whip antenna with an insulating member interposed therebetween. When the radio communication apparatus is waiting for a call, the whip antenna is pushed in the housing of the radio communication apparatus and only the helical antenna is used. On the other hand, when the radio communication apparatus executes communications, the whip antenna is pulled out of the housing and used. Both the whip antenna and helical antenna emit vertically polarized radiation, and are designed to be omnidirectional in a horizontal plane.
However, during communication, mobile communication apparatuses such as portable telephones are used with their housing positioned close to or in contact with a body of the user, in particular, a head, of a user. In this state, the whip antenna is also positioned close to the head of the user. Accordingly, the orientations of the whip antenna in the horizontal and vertical planes are influenced by the body of the user, whereby a side lobe occurs and degrades the directivity of the antenna device.
To prevent this, Jpn. Pat. Appln. KOKAI Publication No. 2000-40910, for example, has proposed a structure in which a slim plate having an end connected to the entirely earthed surface of a circuit board is provided for reducing the current that flows on the ground pattern of the circuit board, thereby suppressing the degradation of the directivity.
However, in this structure, the L-shaped plate is located on the surface of the circuit board close to the head of a user, and has an end connected to the ground pattern at a position remote from the antenna power supply terminal on the circuit board, as is evident from FIGS. 1 to 4 of the publication. Since, in this structure, the plate is positioned close to the head of the user, it is liable to be influenced by the head. Further, since the connection position of the plate with respect to the ground pattern of the circuit board is remote from the antenna power supply terminal, the current flowing to the ground pattern of the circuit board cannot be efficiently guided to the plate. Thus, the conventional structure cannot provide a sufficiently improved effect.